1. Field of the Invention
This present invention relates to cutting blades, particularly to cutting blades having patterns of teeth formed in sequence with repeating patterns throughout the cutting blade and, more particularly, to cutting blades having carbide tips on a steel backer support.
2. Description of Related Art
Many cutting blades rely upon setting the teeth on an angle to expose the tooth tips and allow efficient cutting (FIG. 1C). Setting the teeth also serves to cut a width (called xe2x80x9ckerfxe2x80x9d) which is greater than the thickness of the blade and thereby allow more efficient passage of the blade body through the work. Prior art shows arrangements of these set teeth wherein the magnitude of displacement from the side of the blade varies and creates a broaching type of functionality as the kerf generated by the blade is made wider (see, U.S. Pat. No. 4,727,788 dated Mar. 1, 1988 and U.S. Pat. No. 4,813,324 dated Mar. 21, 1989). When setting the teeth of a blade, it is common to encounter variations (from the intended set) in the magnitude of set and the angle of the set tooth. These variations occur due to minor differences in position of the tooth during setting, variations present in the milling cut that generates the tooth pitch, variations in the mechanical properties of the material, variations in the geometrical characteristics of the blade, variations in the milling cutters used to generate the tooth form, or variations in the setting operation itself. This multitude of variations reduces the chance that the cutting blade will be made to the intended cutting geometry.
One method, which can reduce these variations, involves the use of grinding to generate the required tooth geometry. Grinding is used in high performance products such as a standard triple chip product (see, U.S. Pat. No. 4,011,783 dated Mar. 15, 1977) to various custom ground configurations (see, U.S. Pat. No. 5,425,296 dated Jun. 20, 1965 and U.S. Pat. No. 5,477,763). Although grinding usually increases the cost of the blade, it is effective in reducing variability. This generally increases performance consistency and precision.
A combination of grinding and setting has been used to create blades that will clear a larger kerf than would be permitted with a blade that is only form ground. This type of tooth form (see U.S. Pat. No. 5,331,876 dated Jul. 26, 1994) is still susceptible to the same types of variability mentioned above for standard set type product.
Patents pertaining to the use of grinding to create tooth forms on cutting blades generally have been restricted to creating blades which have symmetrical profiles when the cutting tooth is viewed from the front of the tooth. Exceptions to this statement occur with ground tooth forms such as those shown in U.S. Pat. No. 4,423,553 dated Jan. 3, 1984 which combines a ground or filed tooth form with setting or splaying of the teeth to create a wide cutting kerf. In some cases, this type of ground tooth has been combined with relief grinding of the blade such as is seen with standard ground relief jigsaw blades.
It can be appreciated that improvements in performance can be achieved through greater precision in the manufacture of the product. In addition, performance improvements can be obtained using arrangements of teeth, which cut preferred portions of the workpiece. Ground tooth forms that cut designated chips or areas of the kerf can provide cutting consistency and precision benefiting the end user.
The following patents are related to the present invention as background information. The disclosures of each are hereby incorporated herein by reference:
The present invention provides a cutting tool having an asymmetric ground tooth form, and a method for making the same. Such a tooth form is particularly useful for cutting tools such as band saw blades, circular saws, hacksaws and other saw type products.
In accord with the present invention, a cutting tool comprises a pattern of cutting teeth, each tooth having a carbide tip on a steel support member, the carbide tip having a side relief decreasing the width of the tip from the maximum width toward the steel support member, wherein at least one pair of teeth have an asymmetric ground tooth form that is asymmetric around a center line through a plane equally dividing a maximum width portion of the carbide tip and wherein the carbide tip of the asymmetric ground tooth form has a maximum width that is wider than a maximum width of the steel support member.
The invention relates to geometric shape of the tooth as ground (sometimes referred to herein as xe2x80x9ctooth formxe2x80x9d), i.e., before any setting operation. The tooth form is the cross-sectional shape of the tip of the tooth, as shown, for instance in FIGS. 2C and 2D. The tip is typically a carbide material that is welded to a steel support. The tooth form has a vertical center line (as shown) which bisects a horizontal line having a length equal to the widest dimension of the tooth form. A symmetric tooth form is symmetric about the center line. An asymmetric tooth form is not symmetric about the center line.
The pattern of tooth forms in the cutting tools of this invention offers improved precision over prior art tooth forms by reducing manufacturing variability. This improved precision can provide more consistent performance and a better quality of the cut surface. A characteristic of preferred embodiments of the present invention is a pattern of non-symmetrical form ground tooth profiles, which cut designated chip profiles and thereby cut specific portions of the kerf much like a broaching application. The non-symmetrical ground tooth profile also can alter the distribution of the downfeed cutting force allowing for more aggressive cutting or conversely, cutting at the desired rate with less downfeed pressure.
The tooth form of the present invention can be an improvement to a range of tooth forms that are made by setting teeth in the prior art forms. A preferred embodiment of the present invention provides a tooth pattern having two symmetrically form ground teeth followed by two non-symmetrically form ground teeth. The leading symmetrically form ground teeth are of differing height and width wherein the first is higher and narrower than the second. The following two non-symmetrically form ground teeth are ground so that the first of this pair cuts a chip on the left and the second cuts a chip on the right (which alternatively may be reversed). This pattern of teeth forms a series of five chips before the pattern repeats.
This invention also provides a method of grinding to generate a cutting profile which performs with greater precision than products which rely on a setting operation. Preferred embodiments of this method can offer the advantage of a better surface finish and greater control over the dimensional variations of the cutting profiles. A difference between this invention and the prior art is the generation of non-symmetrical tooth forms by grinding such that a designated edge of the tooth is assigned to cut a chip of a defined area in the cutting profile. These cutting profiles can be provided in various combinations, which can be tailored to provide the optimum cutting operations for the material being cut. Preferably, the pattern of cutting tooth forms of the present invention provides chips of material having cross sections having rectangular dimensions in the range of about 0.002 to about 0.006 inch in height and of about 0.002 to 0.010 inch in width. Harder materials may have smaller chip dimensions and softer materials may have somewhat larger chip dimensions.
Economical production of variable precision ground tooth forms was difficult with mechanically controlled tooth grinders. Recent improvements in computer controlled grinding equipment have allowed grinding a series of teeth having greatly different profiles in a single pass. Examples of equipment presently commercially available to grind a series of variable tooth forms are the UTMA AL801-B and AL804-B.
The method of the present invention also can offer the ability to manufacture product without the time or expense of a setting operation which is normally performed separate from the grinding operations. This reduces the amount of product handling and, hence, the opportunity for in-process damage to occur.
The method of the present invention also can offer the ability to generate precision tooth forms, which have better penetration rates and hence higher productivity. One reason for this improvement is the increase in the relative point loading on a tooth, which has been reduced in section. Teeth which have been ground symmetrically typically have significantly less tooth point loading than teeth which have been reduced in cross section as presented to the work.
Preferred embodiments of the method of the present invention, thus, include the generation of non-symmetrical tooth profiles through the use of grinding to generate side relief angles, top relief angles and corner chamfers or radii. Specifically, the requisite side clearance angle to permit proper cutting action is generated through precision form grinding rather than the less precise method of bending the teeth over (referred to as xe2x80x9csettingxe2x80x9d). Typical side relief angles for tooth forms of the present invention are from about 2 degrees to about 12 degrees off the vertical, preferably from about 3 degrees to about 6 degrees. Typical top relief angles are 0 degrees to about 12 degrees, preferably from about 3 degrees to about 6 degrees. Typical corner chamfers, when utilized, are from about 25 degrees to about 65 degrees, preferably 45 degrees. Corners can also be rounded, as desired.
The grinding also is used to generate non-symmetrical teeth which cut designated chip profiles as one of a series of broach like teeth, each tooth cutting a designated chip thereby achieving a more precise cutting action than can be obtained with a normal set type product.
A unique feature of a preferred embodiment of this invention is the use of a tooth tip, which is of greater thickness than the backer to which it is attached. The tooth tip is then form ground with a side relief to provide for superior cutting action. Previous tooth tips and the state of the art teach forming tooth tips, which begin at the same thickness as the backer and then are either (i) set to either side to create a wider kerf, or (ii) the backer is reduced in thickness to provide relief. By having a tooth tip of greater thickness than the backer, less stock removal is required to create a given amount of clearance (as related to reducing the thickness of the backer). Tip and backer material are well known to those skilled in the art of making cutter tools. For example, the backer material is typically tool steel and the tip material is typically a carbide.
One or more of these modifications can likewise be used to improve the above-described prior art tooth forms, especially those disclosed in U.S. Pat. No. 4,827,855 and WO 98/07545.
Thus, the present invention provides a method for forming non-symmetrical tooth forms which improve upon the performance of set type tooth forms. The tooth forms can include variable profiles and number of teeth to create a precision cutting form.